1. Field of the Invention
This invention relates to a valve having normally open and normally closed ports and in particular to such a valve in which the normally open port can be readily changed to normally closed and vice versa.
2. Discussion of the Prior Art
Valves which have a normally open port and a normally closed port with a common port between the normally open and normally closed ports are well known. Such valves, which are typically solenoid operated, are common and popular for pneumatic and hydraulic fluid control applications.
Such valves typically have a fixed port pattern, and especially in the case of hydraulic valves, the pattern is usually made to match a pattern of ports on a control system mounting block to which the valve is mounted. Thus, the pattern of ports on the valve is dictated by the pattern of ports on the control system mounting block. In addition, many valve manufacturers have adopted their own port patterns, which differ from the port patterns of other manufacturers. Furthermore, it is typical that a normally open port cannot be changed to a normally closed port using the same valve. Instead, a different valve having a different arrangement of internal components must be employed.
Having many different types of valves and many different port configurations has created problems in inventory control of distribution outlets for such valves and in repair and replacement of valves in existing control systems. With many different valves and many different port configurations, each particular valve has a relatively limited application and yet is still desirable to maintain in inventory. In addition, the rather unique application of any particular valve to a particular control system creates difficulties in changing the functions of ports in existing control systems, resulting in a lack of flexibility in adapting existing control systems to different functions or purposes.